The invention relates generally to an optical communication system and, more particularly, to a method and apparatus for determining loss parameters for optical cross-connects.
The use of optical switches in communication networks offers several advantages over conventional electrical switches. For example, optical switches provide connections with reduced insertion loss, high connection-to-connection isolation, relatively fast reconfiguration speed and high degree of bit rate and format independence. Optical cross-connects, which function as optical switches, also allow dynamic wavelength routing within a communication network. There are currently only a few optical switching technologies that are practical for achieving relatively high port counts, e.g., in a range of about 100xc3x97100 to 1000xc3x971000, among which are those based on free-space beam-steering optics.
Beam-steering switches are capable of providing a large number of connections with a single stage because each of the individual input and output ports may be configured to a very large number of statesxe2x80x94e.g., an optical beam from a specific input port may be steered to different angles, thus directing the beam to a large number of output ports. This is in sharp contrast with other Nxc3x97N optical switches built up from either 1xc3x972 or 2xc3x972 multi-stage optical crosspoint elements or 2-stage Nxc3x97N switches based on 1xc3x97N switches, which require both a large number of elements (xcx9cNlog2N to N2) and many switching stages. However, to achieve a high degree of accuracy in angular positioning of the optical beam for beam-steering, some form of feedback is necessary to ensure reliable connections between input and output ports.
One way of targeting and verifying an optical connection is to measure an insertion loss obtained for a particular connection, and compare it to a reference insertion loss associated with that connection. For an optical cross-connect with N input ports and M output ports, for example, existing connection algorithms using reference insertion loss values store the loss parameters in a table with individual entries for each of the possible Nxc3x97M connections within on board memory in controllers. It should be noted that the number of input ports (N) and the number of output ports (M) may be, but does not have to be, equal to each other.
The invention provides generally a method and an apparatus for deriving insertion losses for connections within a single-stage optical cross-connect. In one aspect of the invention, a reduced set of loss parameters, each associated with an individual input or output port, is used to derive insertion losses for connections between any one of the input ports and any one of the output ports. In another aspect of the invention, an apparatus comprises a controller and the reduced set of loss parameters is stored in a memory of the controller. The controller allows insertion losses between any one of the input ports and any one of the output ports to be calculated from the reduced set of loss parameters.